BCECE Engineering BCECE Engineering Solved Paper-2007

  • question_answer
    A variable chord is drawn through the origin to  the circle \[{{x}^{2}}+{{y}^{2}}-2ax=0.\]The locus of the centre of the circle drawn on this chord as diameter is

    A)  \[{{x}^{2}}+{{y}^{2}}+ax=0\]

    B)  \[{{x}^{2}}+{{y}^{2}}-ax=0\]

    C)  \[{{x}^{2}}+{{y}^{2}}+ay=0\]

    D)  \[{{x}^{2}}+{{y}^{2}}-ay=0\]

    Correct Answer: B

    Solution :

    Let \[(h,k)\] be the co-ordinates of the centre of circle of which the given chord is the diameter. Then \[(h,k)\] be mid point of the chord, so, its equation is \[S=T.\] \[{{h}^{2}}+{{k}^{2}}-2ah=hx+ky-a(x+h)\] \[\Rightarrow \]\[x(h-a)+ky={{h}^{2}}+{{k}^{2}}-ah\] If it passes through  \[(0,0),\]  therefore \[{{h}^{2}}+{{k}^{2}}-ah=0\]and the locus of \[(h,k)\] is\[{{x}^{2}}+{{y}^{2}}-ax=0.\]


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